<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
    <style>
        
        .parent{
            width:200px;
            height:200px;
            background: red;

        }
        .child{
            margin-top:50px;
            width:100px;
            height:100px;
            background: green;
        }
        .row:before{
            content:"";
            display: table;

        }
    </style>
</head>
<body>
    <div class="parent row">
        <div class="child"></div>
    </div>
</body>
</html>